On the Biological Occurrence and Regulation of 1-Acyl and 1-O-Alkyl-diradylglycerols in Human Neutrophils

Quantification of pentafluorobenzyl oxime derivatives of long chain aldehydes by GC-MS analysis

Negative ion mass spectrometric techniques, for compounds having good ionization properties, such as pentafluorobenzyl derivatives, are believed to be more sensitive than positive ion methods. Preparation of PFB oximes of fatty aldehydes from crude lipid extracts is problematic due to the release of free aldehydes from plasmalogens during derivatization. Accordingly, in these studies plasmalogens were removed by silicic acid column chromatography prior to pentafluorobenzyl derivatization. This simple purification step to remove plasmalogens is shown to facilitate the quantification of long-chain aldehydes by analysis of their pentafluorobenzyl oxime derivatives utilizing gas chromatography-mass spectrometry in the negative ion chemical ionization mode. The limit of detection for long chain fatty aldehydes using this method is 0.5 pmol and it is linear over two orders of magnitude. Silicic acid column chromatography followed by electrospray ionization mass spectrometry demonstrated that plasmalogens were removed (the detection limit for this analyses was <or=0.3 pmol). Furthermore, we have exploited the utility and sensitivity of this method to identify increases in hexadecanal and octadecanal in 3-amino-1,2,4-triazole treated human neutrophils.

Phosphorothioate analogues of alkyl lysophosphatidic acid as LPA3 receptor-selective agonists

The metabolically stabilized LPA analogue 1-oleoyl-2-O-methyl-rac-glycerophosphorothioate (OMPT) was recently shown to be a potent subtype-selective agonist for LPA3, a G-protein-coupled receptor (GPCR) in the endothelial differentiation gene (EDG) family. Further stabilization was achieved by replacing the sn-1 O-acyl group with an O-alkyl ether. A new synthetic route for the enantiospecific synthesis of the resulting alkyl LPA phosphorothioate analogues is described. The pharmacological properties of the alkyl OMPT analogues were characterized for subtype-specific agonist activity using Ca2+-mobilization assays in RH7777 cells expressing the individual EDG family LPA receptors. Alkyl OMPT analogues induced cell migration in cancer cells mediated through LPA1. Alkyl OMPT analogues also activated Ca2+ release through LPA2 activation but with less potency than sn-1-oleoyl LPA. In contrast, alkyl OMPT analogues were potent LPA3 agonists. The alkyl OMPTs 1 and 3 induced cell proliferation at submicromolar concentrations in 10T 1/2 fibroblasts. Interestingly, the absolute configuration of the sn-2 methoxy group of the alkyl OMPT analogues was not recognized by any of the LPA receptors in the EDG family. By using a reporter gene assay for the LPA-activated nuclear transcription factor PPARgamma, we demonstrated that phosphorothioate diesters have agonist activity that is independent of their ligand properties at the LPA-activated GPCRs. The availability of new alkyl LPA analogues expands the scope of structure-activity studies and will further refine the molecular nature of ligand-receptor interactions for this class of GPCRs.

Enhanced superoxide release and elevated protein kinase C activity in neutrophils from diabetic patients: association with periodontitis

Inflammation and oxidative stress are important factors in the pathogenesis of diabetes and contribute to the pathogenesis of diabetic complications. Periodontitis is an inflammatory disease that is characterized by increased oxidative stress, and the risk for periodontitis is increased significantly in diabetic subjects. In this study, we examined the superoxide (O(2)(-))-generating reduced nicotinamide adenine dinucleotide phosphate-oxidase complex and protein kinase C (PKC) activity in neutrophils. Fifty diabetic patients were grouped according to glycemic control and the severity of periodontitis. Neutrophils from diabetic patients with moderate [amount of glycated hemoglobin (HbA(1c)) between 7.0% and 8.0%] or poor (HbA(1c) >8.0%) glycemic control released significantly more O(2)(-) than neutrophils from diabetic patients with good glycemic control (HbA(1c) <7.0%) and neutrophils from nondiabetic, healthy individuals upon stimulation with 4beta-phorbol 12-myristate 13-acetate or N-formyl-Met-Leu-Phe. Depending on glycemic status, neutrophils from these patients also exhibited increased activity of the soluble- and membrane-bound forms of PKC, elevated amounts of diglyceride, and enhanced phosphorylation of p47-phox during cell stimulation. In addition, we report a significant correlation between glycemic control (HbA(1c) levels) and the severity of periodontitis in diabetic patients, suggesting that enhanced oxidative stress and increased inflammation exacerbate both diseases. Thus, hyperglycemia can lead to a novel form of neutrophil priming, where elevated PKC activity results in increased phosphorylation of p47-phox and O(2)(-) release.

Induction of 5-lipoxygenase activation in polymorphonuclear leukocytes by 1-oleoyl-2-acetylglycerol

1,2-Diacylglycerols (DAGs) can prime polymorphonuclear leukocytes (PMNL) for enhanced release of arachidonic acid (AA) and generation of 5-lipoxygenase (5-LO) products upon subsequent agonist stimulation. Here, we demonstrate that in isolated human PMNL, 1-oleoyl-2-acetylglycerol (OAG) functions as a direct agonist stimulating 5-LO product formation (up to 42-fold). OAG caused no release of endogenous AA, but in the presence of exogenous AA, the magnitude of 5-LO product synthesis induced by OAG was comparable to that obtained with the Ca(2+)-ionophore A23187. Interestingly, OAG-induced 5-LO product synthesis was not connected with increased 5-LO nuclear membrane association. Examination of diverse glycerides revealed that the sn-2-acetyl-group is important, thus, also 1-O-hexadecyl-2-acetylglycerol (EAG) stimulated 5-LO product formation (up to 8-fold). Treatment of PMNL with OAG did not alter the mobilization of Ca(2+) but removal of intracellular Ca(2+) abolished the upregulatory OAG effects. Notably, the PKC activator phorbol-myristate-acetate hardly increased 5-LO product synthesis and PKC inhibitors failed to suppress the effects of OAG. Although OAG rapidly activated p38 MAPK and p42/44(MAPK), which can stimulate 5-LO for product synthesis, specific inhibitors of these kinases could not prevent 5-LO activation by OAG. Together, OAG acts as a direct agonist for 5-LO product synthesis in PMNL stimulating 5-LO by novel undefined mechanisms.

Resveratrol inhibits the formation of phosphatidic acid and diglyceride in chemotactic peptide- or phorbol ester-stimulated human neutrophils

Resveratrol (trans-3,5,4'-trihydroxystilbene, Res) is a naturally occurring antioxidant found in grape berry skins and red wine. It has anti-inflammatory effects. In this study, we examined the effect of Res on the formation of phosphatidic acid (PA) and diglyceride (DG), in human neutrophils stimulated by formyl-methionyl-leucyl-phenylalanine (fMLP) or by phorbol 12-myristate 13-acetate (PMA). We measured the masses of PA and DG by using a nonradioactive method. Our results showed that Res inhibited the formation of PA in a concentration dependent manner with an IC(50) value of 42.4 and 60.9 microM in fMLP- and PMA-stimulated cells, respectively. Res also suppressed the formation of phosphatidylethanol (PEt), thereby implying inhibition of phospholipase D (PLD) activity. In addition, Res inhibited the formation of both diacylglycerol (DAG) and ether-linked acylglycerol (EAG) induced by fMLP and by PMA. Our results suggest that Res inhibition of PLD activity may contribute to its anti-inflammatory effects.

Sphingosine Blocks Human Polymorphonuclear Leukocyte Phagocytosis Through Inhibition of Mitogen-Activated Protein Kinase Activation

In the present study, we investigated the mechanism by which sphingosine and its analogues, dihydrosphingosine and phytosphingosine, inhibit polymorphonuclear leukocyte (PMN) phagocytosis of IgG-opsonized erythrocytes (EIgG) and inhibit ERK1 and ERK2 phosphorylation. We used antibodies that recognized the phosphorylated forms of ERK1 (p44) and ERK2 (p42) (extracellular signal-regulated protein kinases 1 and 2). Sphingoid bases inhibited ERK1 and ERK2 activation and phagocytosis of EIgG in a concentration-dependent manner. Incubation with glycine, N,N′-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-bis[(acetyloxy)methyl]ester (BAPTA,AM), an intracellular chelator of calcium, failed to block either phagocytosis or ERK1 and ERK2 phosphorylation, consistent with the absence of a role for a calcium-dependent protein kinase C (PKC) in ERK1 and ERK2 phosphorylations. Western blotting demonstrated that sphingosine inhibited the translocation of Raf-1 and PKCδ from PMN cytosol to the plasma membrane during phagocytosis. These data are consistent with the interpretation that sphingosine regulates ERK1 and ERK2 phosphorylation through inhibition of PKCδ, and this in turn leads to inhibition of Raf-1 translocation to the plasma membrane. Consistent with this interpretation, the sphingosine-mediated inhibition of phagocytosis, ERK2 activation, and PKCδ translocation to the plasma membrane could be abrogated with a cell-permeable diacylglycerol analog. The increase in the diacylglycerol mass correlated with the translocation of PKCδ and Raf-1 to the plasma membrane by 3 minutes after the initiation of phagocytosis. Additionally, the diacylglycerol analog enhanced phagocytosis by initiating activation of PKCδ and its translocation to the plasma membrane. Because PMN generate sufficient levels of sphingosine by 30 minutes during phagocytosis of EIgG to inhibit phagocytosis, it appears that sphingosine can serve as an endogenous regulator of EIgG-mediated phagocytosis by downregulating ERK activation.

Sphingosine Blocks Human Polymorphonuclear Leukocyte Phagocytosis Through Inhibition of Mitogen-Activated Protein Kinase Activation

In the present study, we investigated the mechanism by which sphingosine and its analogues, dihydrosphingosine and phytosphingosine, inhibit polymorphonuclear leukocyte (PMN) phagocytosis of IgG-opsonized erythrocytes (EIgG) and inhibit ERK1 and ERK2 phosphorylation. We used antibodies that recognized the phosphorylated forms of ERK1 (p44) and ERK2 (p42) (extracellular signal-regulated protein kinases 1 and 2). Sphingoid bases inhibited ERK1 and ERK2 activation and phagocytosis of EIgG in a concentration-dependent manner. Incubation with glycine, N,N′-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-bis[(acetyloxy)methyl]ester (BAPTA,AM), an intracellular chelator of calcium, failed to block either phagocytosis or ERK1 and ERK2 phosphorylation, consistent with the absence of a role for a calcium-dependent protein kinase C (PKC) in ERK1 and ERK2 phosphorylations. Western blotting demonstrated that sphingosine inhibited the translocation of Raf-1 and PKCδ from PMN cytosol to the plasma membrane during phagocytosis. These data are consistent with the interpretation that sphingosine regulates ERK1 and ERK2 phosphorylation through inhibition of PKCδ, and this in turn leads to inhibition of Raf-1 translocation to the plasma membrane. Consistent with this interpretation, the sphingosine-mediated inhibition of phagocytosis, ERK2 activation, and PKCδ translocation to the plasma membrane could be abrogated with a cell-permeable diacylglycerol analog. The increase in the diacylglycerol mass correlated with the translocation of PKCδ and Raf-1 to the plasma membrane by 3 minutes after the initiation of phagocytosis. Additionally, the diacylglycerol analog enhanced phagocytosis by initiating activation of PKCδ and its translocation to the plasma membrane. Because PMN generate sufficient levels of sphingosine by 30 minutes during phagocytosis of EIgG to inhibit phagocytosis, it appears that sphingosine can serve as an endogenous regulator of EIgG-mediated phagocytosis by downregulating ERK activation.

Differential activation of human neutrophil cytosolic phospholipase A2 and secretory phospholipase A2 during priming by 1,2-diacyl- and 1-O-alkyl-2-acylglycerols

We have shown previously that both 1,2-diacylglycerol (AAG) and 1-O-alkyl-2-acylglycerol (EAG) prime neutrophil release of arachidonic acid via uncharacterized phospholipases A2. Therefore, we investigated the actions of EAG and AAG specifically on neutrophil cytosolic (cPLA2) and secretory (sPLA2) phospholipase A2s. We hypothesized that AAG as a protein kinase activator would activate cPLA2 via phosphorylation events. EAG is antagonistic to the AAG activation of PKC, thus it was not expected to act via phosphorylation of cPLA2. Neutrophils were primed with either AAG or EAG and then stimulated with fMLP. When neutrophils were primed with 5-20 microM 1,2-diacylglycerol, a shift was observed in cPLA2 migration on SDS-PAGE gels, consistent with phosphorylation of the protein. This gel shift was not seen after exposure to EAG. AAG also caused a parallel increase in enzymatic activity of cPLA2 that was not seen with EAG. We also investigated whether either diglyceride would cause similar priming or direct secretion of sPLA2. Both AAG and EAG directly caused significant secretion of neutrophil sPLA2. EAG also increased the release of sPLA2 in cells subsequently stimulated with fMLP. Thus, AAG activated cPLA2 and stimulated secretion of sPLA2. In contrast, EAG did not activate cPLA2, but directly activated secretion of sPLA2. We also demonstrated that human synovial fluid sPLA2 increased AA release from resting and fMLP-stimulated neutrophils. Given that diglycerides prime for release of AA, PAF, and LTB4, these current data support the hypothesis that such priming may be mediated by phosphorylation dependent (cPLA2) or phosphorylation independent (e.g. secretion of sPLA2) events.

Translocation of protein kinase C isoforms in rat neutrophils

In this study, we examined the protein kinase C (PKC) isoforms present in cytosol and membrane fractions of rat neutrophils by Western blotting analysis with monoclonal antibodies against PKC isoforms and demonstrated that rat neutrophils express at least three conventional PKCs (cPKC), alpha, beta and gamma, four novel PKCs (nPKC), delta, epsilon, theta and mu, and three atypical PKCs (aPKC), iota, lambda and zeta, although PKC lambda and zeta were barely detected. Cells stimulated with phorbol 12-myristate 13-acetate (PMA) induce a sustained and marked translocation of cPKC and nPKC from the cytosol to particulate fraction. A concentration-dependence of PMA on the membrane translocation of PKC isoforms was observed. Treatment with formyl-Met-Leu-Phe (fMLP), in contrast with PMA, caused a transient and less prominent association of cPKC and nPKC with particulate fraction. However, the distribution of PKC iota isoform was affected neither by fMLP nor by PMA. These data indicate that the rat neutrophils contain PKCs of three isoform families and the membrane translocation of cPKC and nPKC was observed in cells in response to PMA as well as to fMLP.

Ceramide inhibits phospholipase D in a cell-free system

Recent evidence in whole cells has implicated ceramide in the regulation of phospholipase D (PLD). In intact HL-60 cells, phorbol myristate acetate (PMA) activated PLD as measured by [3H]palmitate-labeled phosphatidylcholine conversion to phosphatidylethanol in the presence of 2% ethanol. C6-Ceramide completely inhibited PLD activation after 4 h of treatment and was maximally active at 10 microM. The activity was structurally specific in that the structural analogs 4,5-dihydro-C6-ceramide and dioctanoylglycerol were inactive. Although ceramide inhibited PMA-induced activation of PLD, it did not inhibit translocation of protein kinase C (PKC) to the membrane in response to PMA. In a cell-free system, we confirmed that PLD is activated by guanosine 5'-O-(3-thiotriphosphate (GTPgammaS); however, ceramide had no effect on this activity under a variety of conditions. Activation of PLD by GTPgammaS was synergistically enhanced by the addition of PKC activators. This upstream effect was inhibited rapidly and specifically by ceramide (30 microM). Recombinant ARF plus PKCalpha substituted for crude cytosol in the activation of PLD, and this activity was inhibited by C6-ceramide. Taken together, these data show that ceramide interferes with PKC-mediated activation of PLD.

Phospholipase D-derived products in the regulation of 12-O-tetradecanoylphorbol-13-acetate-stimulated prostaglandin synthesis in madin-darby canine kidney cells

Madin-Darby canine kidney (MDCK) cells stimulated with 12-O-tetradecanoylphorbol-13-acetate (TPA) in the presence of ethanol synthesize phosphatidylethanol (PEt) instead of phosphatidic acid (PA) and diglyceride (DG). We have used ethanol to block the production of phospholipase D (PLD)-derived PA and DG (from PA hydrolysis) to study their role in signal transduction. In MDCK cells, TPA-stimulated prostaglandin E2 (PGE2) synthesis was inhibited by ethanol at concentrations which inhibit PA and DG formation. In addition, TPA elicited a prolonged increase in PGE2 synthesis that is dependent upon continuous activation of PLD. The TPA-stimulated translocation of protein kinase Calpha (PKCalpha) from cytosol to membrane was unaffected by ethanol. This suggests that PLD-derived products act downstream of PKC in TPA-stimulated prostaglandin synthesis. The calcium ionophore, A23187, did not activate PLD, and PGE2 synthesis in response to A23187 was unaffected by ethanol. TPA increased prostaglandin endoperoxide H synthase (PGHS) activity and increased the amount of immunodetectable prostaglandin endoperoxide H synthase 2 (PGHS-2). A23187 did not induce PGHS-2 and A23187-stimulated PGE2 synthesis appears to be due to the constitutively expressed PGHS-1. Blocking the formation of PLD-derived products, PA and DG, inhibited the induction of PGHS-2 by TPA. These results indicate that prolonged PGE2 synthesis in response to TPA is due to the continuous induction of PGHS-2, which is dependent upon PLD activation. In contrast, induction of PGHS-2 by epidermal growth factor was not affected by ethanol. Epidermal growth factor did not induce PKCalpha translocation nor activate PLD. Taken together, these data suggest that PLD-derived PA or DG act as second messengers in the induction of PGHS-2 by PKC-dependent pathways. The demonstration that inhibition of TPA-induced PA formation inhibits Raf-1 translocation in MDCK cells (Ghosh, S., Strum, J. C., Sciorra, V. A., Daniel, L. W. , and Bell, R. M. (1996) J. Biol. Chem. 271, 8472-8480) suggests that PA is the active PLD metabolite in TPA-stimulated signaling.

Diradylglycerol formation in cholecystokinin-stimulated rabbit pancreatic acini. Assessment of precursor phospholipids by means of molecular species analysis

The aim of the present study was to assess the origin of the 1,2-diradylglycerols produced during prolonged hormonal stimulation of rabbit pancreatic acini by comparison of their relative molecular species composition with that of the major acinar phospholipids. Both phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) consisted of 1,2-diacyl as well as 1-alk-1-2-acyl species. In contrast, phosphatidylinositol (PtdIns), phosphatidylserine and phosphatidic acid existed only in the 1,2-diacyl form. Acinar cells did not contain detectable amounts of 1-alkyl-2-acyl phospholipids. Similarly, the acinar 1,2-diradylglycerol fraction consisted of 1,2-diacylglycerols and 1-alk-1-enyl-2-acylglycerols. Mass 1,2-diradylglycerol measurements revealed that prolonged stimulation with cholecystokinin resulted in a marked and sustained increase in acinar 1,2-diradylglycerol content. Based on the relative amounts of the 1,2-diacyl species present in both the 1,2-diradylglycerol fraction and the individual phospholipids, it is calculated that under control conditions 60% of the 1,2-diacylglycerols originate from PtdCho and 40% from PtdIns, whereas under stimulatory conditions 53% is calculated to be derived from PtdCho, 46% from PtdIns and 1% from PtdEtn. Likewise, it is calculated that in control as well as stimulated acini 100% of the 1-alk-l-enyl-2-acylglycerols originate from plasmenylcholine. Further evidence in favour of the idea that at least a considerable part of the 1,2-diacylglycerols produced during prolonged hormonal stimulation originate from inositolphospholipids is provided by the observation that labeling of phosphatidylinositol 4,5-bisphosphate with inorganic phosphate reached isotopic equilibrium markedly faster under stimulatory conditions as compared to the control situation, which is in agreement with an elevated turnover rate. The data presented support the idea that PtdCho and inositolphospholipids are the major precursors in basal and stimulated 1,2-diradylglycerol production in rabbit pancreatic acini.

Phospholipid molecular species composition of developing fetal guinea pig brain

Adequate accumulation of polyunsaturated essential fatty acids, in particular docosahexaenoic acid (22:6n-3), into membrane phospholipids is critical for optimal fetal brain development. This process is maximal during the period of rapid neurite outgrowth, neuritogenesis, which precedes the major growth phase, myelination. There is no information about differential changes during gestation to individual brain phospholipid molecular species which contain 22:6n-3. Such details of brain development would be concealed by total fatty acid analysis of isolated phospholipid classes. We have detailed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecular species compositions in developing fetal guinea pig brain. Total brain PC concentration increased substantially between 40 and 68 (term) d of gestation, corresponding to myelination, while PE increased in a biphasic manner between 25-35 d, which was coincident with onset of neuritogenesis, and 40-68 d. Fetal brain development was accompanied by complex changes in the concentration of individual phospholipid molecular species. During early gestation (25-40 d) 22:6n-3 was enriched in both PC and PE sn-1 16:0 molecular species. However, between 40 d and term there was no further increase in brain PC 22:6n-3 content, while brain PE was significantly enriched in both PE18:1/22:6 and PE18:0/22:6. We hypothesize that accumulation of 22:6n-3 into sn-1 18:1 and 18:0 species represents establishment of a 22:6n-3-containing membrane PE pool which may be turned over more slowly than sn-1 16:0 species. Identification of specific changes in membrane phospholipids which are associated with defined events in brain development may provide a basis for assigning functional roles to individual molecular species.

Effect of maternal ethanol consumption during pregnancy on the phospholipid molecular species composition of fetal guinea-pig brain, liver and plasma

The effect of maternal ethanol consumption during pregnancy upon accumulation of docosahexaenoic acid (22:6(n - 3)) into developing brain phospholipids was determined in a guinea-pig model of fetal alcohol syndrome. Feeding adult guinea-pigs 6 g/kg per day ethanol both before and throughout pregnancy was associated with decreased 22:6(n - 3) concentration in both fetal brain phosphatidylcholine (PC) and phosphatidylethanolamine (PE) at 40/68 days gestation and at term. Since adequate assimilation of 22:6(n - 3) into fetal brain is critical for optimal neuronal development, reduced accumulation of 22:6(n - 3) into phospholipids may be one important mechanism for ethanol-induced brain damage. Liver from ethanol-exposed fetuses contained significantly lower concentrations of both PC and PE 22:6(n - 3)-containing molecular species. However, there was no difference in plasma PC polyunsaturated fatty acid content in ethanol-exposed fetuses compared with controls. One possible explanation for impaired 22:6(n - 3) accumulation into ethanol-exposed fetal brain phospholipids may be the result of the action of inappropriate mechanisms which counteract ethanol-induced increased membrane fluidity by reducing the polyunsaturated fatty acid content of brain phospholipids.

Inhibition of phorbol ester-stimulated arachidonic acid release by alkylglycerols

Although synthetic analogs of alkylglycerol (AG), such as dodecylglycerol, possess potent biological activities, their mechanism of action has not been determined. We recently detected substantial amounts of AG in unstimulated MDCK cells (Warne, T.R. and Robinson, M. (1991) Anal. Biochem. 198, 302-307) raising the possibility that the endogenous compound may act as a biological mediator. In this study, we examined the effects of synthetic AG on the release of arachidonic acid and arachidonate metabolites (AA) from Madin Darby canine kidney (MDCK) cells in response to 12-O-tetradecanoylphorbol-13-acetate (TPA) in order to characterize its effects on this signalling pathway. Treatment of MDCK with AG potently inhibited the release of AA during subsequent stimulation with TPA. Dodecylglycerol, the most effective of a series of alkyglycerols tested, was active at concentrations as low as 3 microM. The sn-1 and sn-3 forms of AG were found to be equally potent inhibitors. The effects of AG on AA release were not the result of arachidonic acid redistribution among cellular lipids and were independent of the phospholipid source of the released AA. AG did not inhibit the release of AA from MDCK cells when bradykinin was used as a stimulus, indicating selectivity for the effects produced by phorbol esters. These results show that AG can function as a potent and specific inhibitor of TPA-mediated AA release. The ability of AG to regulate this signalling pathway in intact MDCK cells, together with its natural occurrence, suggests a potential bioregulatory role for the endogenous compound as an inhibitor of protein kinase C.

Inhibition by gomisin C (a lignan from Schizandra chinensis) of the respiratory burst of rat neutrophils

1. The possible mechanisms of action of the inhibitory effect of gomisin C on the respiratory burst of rat neutrophils in vitro was investigated. 2. The peptide formyl-Met-Leu-Phe (FMLP) induced superoxide anion (O2-) formation and O2 consumption, which was inhibited by gomisin C in a concentration-dependent manner (IC50 21.5 +/- 4.2 micrograms ml-1 for O2- formation). Gomisin C also suppressed O2- formation and consumption at low concentrations of phorbol myristate acetate (PMA) with an IC50 value of 26.9 +/- 2.1 micrograms ml-1 for O2- formation. However, gomisin C did not affect the responses induced by a high concentration of PMA. 3. Gomisin C had no effect on O2- generation and uric acid formation in the xanthine-xanthine oxidase system, and failed to alter O2- generation during dihydroxyfumaric acid (DHF) autoxidation, indicating that it does not scavenge superoxide. 4. Like trifluoperazine (TFP), gomisin C attenuated the activity of PMA-activated neutrophil particulate NADPH oxidase in a concentration-dependent manner. 5. Gomisin C reduced the elevations of cytosolic free Ca2+ in neutrophils stimulated by FMLP in the presence or absence of EDTA. Cyclopiazonic acid (CPA) induced the release of Ca2+ from intracellular stores and this was also reduced by gomisin C. However, the Ca2+ influx pathway activated by CPA was not affected by gomisin C. 6. The cellular cyclic AMP level was markedly increased by forskolin, but not by gomisin C. Moreover, the inositol phosphate levels in FMLP-activated neutrophils were not affected by gomisin C. 7. These results show that the inhibitory action of gomisin C on the respiratory burst is not mediated by changes in cellular cyclic AMP or in inositol phosphates, or by scavenging O2- released from neutrophils, but may be mediated partly by the suppression of NADPH oxidase and partly by the decrease of cytosolic Ca2+ released from an agonist-sensitive intracellular store.

Purified dietary n-3 polyunsaturated fatty acids alter diacylglycerol mass and molecular species composition in concanavalin A-stimulated murine splenocytes

A low-dose, short-term dietary supplementation with highly purified (n-3) fatty acid ethyl esters was studied in mice to determine the effect on splenic cell membrane diacylglycerol mass and composition. Mice were fed diets containing either 3% safflower oil (SAF) ethyl esters, 2% SAF plus 1% eicosapentaenoic acid ethyl ester (EPA), or 2% SAF plus 1% docosahexaenoic acid ethyl ester (DHA). Following a 10-day feeding period, pathogen-free mice were sacrificed and splenic cells isolated and stimulated with concanavalin A (Con A) at 10 micrograms/ml. After 0 min (basal), 5 min, and 180 min, 1,2-diacyl, 1-O-alkyl-2-acyl, and 1-O-alkenyl-2-acyl-sn-glycerol subclasses were isolated and quantitated by HPLC. Diacylglycerol (DAG) was found to be the major diradylglycerol (DG) component in murine splenocytes. DHA-fed mice had significantly (P < 0.05) higher levels of DAG at all stimulation time points relative to EPA and SAF animals. Significant effects (P < 0.05) of diet, time, and a diet x time interaction (P < 0.05) were noted for various DAG molecular species. In general, a significantly higher (n-3) polyunsaturated fatty acid (PUFA) content in the EPA and DHA groups, and a significantly higher (n-6) PUFA content in the SAF group was noted. 18:0-22:5(n-3), 18:1-22:5(n-3) and 16:1-20:5(n-3) species were present only in EPA and DHA-DAG, confirming the incorporation of (n-3) fatty acids into splenocyte DAG. The data indicate that the molecular species composition of murine splenocyte DAG is significantly modulated by low-dose, short-term EPA and DHA feeding. In addition, substitution of SAF with DHA results in an increase in DAG mass. These alterations could potentially influence signal transduction pathways regulating lymphocyte function.

Changes in bioactive lipids, alkylacylglycerol and ceramide, occur in HIV-infected cells

The mass levels of bioactive lipids known to modulate signal transduction or to possess other biological activities were measured in HIV-infected CEM cells. The levels of diacylglycerol, an activator of protein kinase C, as well as of alkylacylglycerol were elevated. A more drastic increase was observed in the ceramide levels after HIV-infection, whereas sphingosine levels were hardly influenced. Interestingly, the magnitude of the changes was related to the infection time, being higher at 8 days after infection then at 4 days. The possible role of these lipids in the cytopathic effects of HIV-infection is discussed. In addition, an improved methodology to quantitate simultaneously diacylglycerol and alkylacylglycerol in crude lipid extracts, based upon their phosphorylation by E. coli diacylglycerol kinase, is presented.

Altered diacylglycerol level and metabolism in neutrophils from patients with localized juvenile periodontitis

Diacylglycerol, a physiological activator of protein kinase C, was elevated nearly twofold in unstimulated peripheral blood neutrophils from patients with localized juvenile periodontitis compared with cells from normal individuals. These cells also showed an enhanced and prolonged elevation of diglyceride in response to N-formylmethionylleucylphenylalanine. The metabolism of a cell-permeant diacylglycerol by diglyceride kinase was significantly decreased, because of a fivefold or higher elevation in the apparent Km of cellular diglyceride kinase.

Cell-free translocation of recombinant p47-phox, a component of the neutrophil NADPH oxidase: effects of guanosine 5'-O-(3-thiotriphosphate), diacylglycerol, and an anionic amphiphile

We reported previously that diacylglycerol (diC8) and GTP gamma S synergize with an anionic amphiphile such as sodium dodecyl sulfate (SDS) to produce high rates of superoxide generation in a cell-free system consisting of neutrophil plasma membrane plus cytosol [Burnham, D. N., Uhlinger, D. J., & Lambeth, J. D. (1990) J. Biol. Chem. 265, 17550-17559]. Here we investigate the effects of these activating factors on the plasma membrane association in an in vitro translated radiolabeled recombinant p47-phox protein. Apparent translocation, assayed by cosedimentation with plasma membranes, required the presence of excess cytosol and an anionic amphiphile, was enhanced by both GTP gamma S and diC8, and was inhibited by high salt, correlating qualitatively with activation; up to 70% cosedimentation was observed with the combination of activators (compared with less than 20% in their absence). Similar results were obtained using heat-inactivated cytosol, wherein another oxidase component, p67-phox, has been inactivated. Unexpectedly, from 50 to 80% of the apparent translocation occurred in the absence of membranes, indicating that protein aggregation accounted for a significant part of the observed translocation. Nevertheless, the percent translocation was increased in all cases by the presence of membranes, indicating some degree of protein-membrane interaction. While a control in vitro translated protein failed to translocate, cosedimentation of p47-phox occurred equally well when red blood cell or neutrophil plasma membranes lacking cytochrome b558 were used. Also, the peptide RGVHFIF, which is contained within the C-terminus of the large subunit of cytochrome b558, failed to inhibit translocation/aggregation of p47-phox, despite its ability to inhibit cell-free activation of the oxidase. The data are consistent with the following: (a) SDS, diC8, and GTP gamma S all act on cytosolic components to alter protein-protein and/or protein-membrane associations, and these changes are necessary (but not sufficient) for activation; (b) these altered associations are likely to function by increasing the local concentration of p47-phox and other components at the plasma membrane; (c) a high background of nonspecific associations in the cell-free activation system is likely to obscure any specific, functionally relevant associations (e.g., with cytochrome b558); and (d) the mechanism of translocation in the cell-free system differs from that seen in intact neutrophils.

The superoxide-generating oxidase of phagocytic cells. Physiological, molecular and pathological aspects

Professional phagocytes (neutrophils, eosinophils, monocytes and macrophages) possess an enzymatic complex, the NADPH oxidase, which is able to catalyze the one-electron reduction of molecular oxygen to superoxide, O2-. The NADPH oxidase is dormant in non-activated phagocytes. It is suddenly activated upon exposure of phagocytes to the appropriate stimuli and thereby contributes to the microbicidal activity of these cells. Oxidase activation in phagocytes involves the assembly, in the plasma membrane, of membrane-bound and cytosolic components of the oxidase complex, which were diassembled in the resting state. One of the membrane-bound components in resting phagocytes has been identified as a low-potential b-type cytochrome, a heterodimer composed of two subunits of 22-kDa and 91-kDa. The link between NADPH and cytochrome b is probably a flavoprotein whose subcellular localization in resting phagocytes remains to be determined. Genetic defects in the cytochrome b subunits and in the cytosolic factors have been shown to be the molecular basis of chronic granulomatous disease, a group of inherited disorders in the host defense, characterized by severe, recurrent bacterial and fungal infections in which phagocytic cells fail to generate O2- upon stimulation. The present review is focused on recent data concerning the signaling pathway which leads to oxidase activation, including specific receptors, the production of second messengers, the organization of the oxidase complex and the molecular defects responsible for granulomatous disease.

A method for the simultaneous determination of alkylacylglycerol, diacylglycerol, monoalkylglycerol, monoacylglycerol, and cholesterol by high-performance liquid chromatography

We describe a method for the quantitative analysis of the individual subclasses (1-O-alkyl and 1-acyl) of diradylglycerols and monoradylglycerols. These lipids, along with cholesterol, were separated from other neutral and polar lipids on silica columns and analyzed by normal-phase high-performance liquid chromatography (HPLC) as their benzoate derivatives. Cholesterylbenzoate, alkylacylglycerolbenzoate, diacylglycerolbenzoate, monoalkylglyceroldibenzoate, and monoacylglyceroldibenzoate eluted from HPLC in five distinct zones. The derivatives of diradylglycerols and monoradylglycerols were further separated within each discrete zone on the basis of the total number of aliphatic carbons at the sn-1 and sn-2 positions. Radiolabeled cholesterol and dihexadecanoylglycerol were used to monitor recovery. Amounts of synthetic alkylacylglycerol, diacylglycerol, monoalkylglycerol, and monoacylglycerol as low as 0.2 nmol per subclass could be accurately quantified. The technique was used to determine the content of diradylglycerol and monoradylglycerol subclasses in Madin-Darby canine kidney and CFTL-12 mast cells. This method should prove useful for the quantitation of lipid second messengers in cultured cells.

Sources of diradylglycerols generated during cell growth and phorbol ester stimulation in Madin-Darby canine kidney cells

The molecular species of diacylglycerol and alkylacylglycerol of Madin-Darby canine Kidney (MDCK) cells were analyzed to determine the sources of diradylglycerols generated during cell growth and phorbol ester stimulation. MDCK cells in log phase growth contained higher levels of diacylglycerol and alkylacylglycerol than confluent cells. Both subclasses of diradylglycerol showed higher levels of saturated and monoenoic species during log phase. Glycerol incorporation into diradylglycerols was increased during growth, consistent with an increase in their synthesis de novo. Stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent activator of protein kinase C, caused an increase in the level of diacylglycerol but not alkylacylglycerol. Log phase MDCK cells showed a greater response to TPA treatment than confluent cells. The molecular species of diacylglycerol generated during stimulation with either TPA or dioctanoylglycerol closely resembled the species of phosphatidylcholine. These results indicate that TPA and synthetic diacylglycerol stimulate endogenous diacylglycerol production through the hydrolysis of phosphatidylcholine. In contrast, the higher content of diacylglycerol and alkylacylglycerol in replicating MDCK cells is the result of an increase in their synthesis de novo.

Source and role of diacylglycerol formed during phagocytosis of opsonized yeast particles and associated respiratory burst in human neutrophils

The results presented in this paper demonstrate that in human neutrophils phagocytosis of C3b/bi and IgG-opsonized yeast particles is associated with activation of phospholipase D and that this reaction is the main source of diglycerides. The demonstration is based upon the following findings: 1) the challenge of neutrophils with these opsonized particles was followed by a rapid formation of [3H]alkyl-phosphatidic acid [( 3H]alkyl-PA) and [3H]alkyl-diglyceride [( 3H]alkyl-DG) in cells labeled with [3H]alkyl-lyso-phosphatidylcholine; 2) in the presence of ethanol [3H]alkyl-phosphatidylethanol was formed, and accumulation of [3H]alkyl-PA and [3H]alkyl-DG was depressed; 3) propranolol, by inhibiting the dephosphorylation of [3H]alkyl-PA, completely inhibited the accumulation of [3H]alkyl-DG and depressed by about 75% the formation of diglyceride mass. Evidence is also presented that phagocytosis of C3b/bi and IgG-opsonized yeast particles and associated respiratory burst can take place independently of diglyceride formation and of the activity of this second messenger on protein kinase C. In fact: a) propranolol while completely inhibited the formation of diglyceride mass did not modify either the phagocytosis or respiratory burst; b) these two processes were insensitive to staurosporine.

Divergent effects of propranolol on neutrophil superoxide release: involvement of phosphatidic acid and diacylglycerol as second messengers

Relatively high levels of propranolol (170 microM) markedly attenuated the generation of 1,2 diacylglycerol in neutrophils stimulated with either FMLP plus cytochalasin B or with 20.0 mM NaF. This effect resulted from inhibition of phosphatidic acid phosphohydrolase as it was accompanied by a corresponding increase in the recovery of phosphatidic acid in organic extracts of stimulated cells. Although propranolol enhanced phosphatidic acid levels in neutrophils treated with FMLP alone, the drug had only a slight inhibitory influence on diglyceride generation in these cells. The effect of propranolol on enhancement of PA levels in neutrophils treated with FMLP alone strongly correlated with enhancement of FMLP-induced O2- generation. However, propranolol induced a similar dose-dependent inhibition of O2- generation in neutrophils stimulated with either FMLP + cytochalasin B or with 20.0 mM NaF. These results are consistent with the hypothesis that both phosphatidic acid and diacylglycerol are required for optimal initiation of neutrophil O2- release.

Epidermal growth factor-induced hydrolysis of phosphatidylcholine by phospholipase D and phospholipase C in human dermal fibroblasts

The enzymatic pathways for formation of 1,2-diradylglyceride in response to epidermal growth factor in human dermal fibroblasts have been investigated. 1,2-Diradylglyceride mass was elevated 2-fold within one minute of addition of EGF. Maximal accumulation (4-fold) occurred at 5 minutes. Since both diacyl and ether-linked diglyceride species occur naturally and may accumulate following agonist activation, we developed a novel method to determine separately the alterations in diacyl and ether-linked diglycerides following stimulation of fibroblasts with EGF. Utilizing this method, it was found that approximately 80% of the total cellular 1,2-diradylglyceride was diacyl, the remaining 20% being ether-linked. Addition of EGF caused accumulation of 1,2-diacylglyceride without alteration in the level of ether-linked diglyceride. Thus, the observed induction of 1,2-diradylglyceride by EGF was due exclusively to increased formation of 1,2-diacylglyceride. In cells labelled with [3H]choline, the water soluble phosphatidylcholine hydrolysis products, phosphorylcholine and choline, were increased 2-fold within 5 minutes of addition of EGF. No hydrolysis of phosphatidylethanolamine, phosphatidylserine, or phosphatidylinositol was observed. Quantitation by radiolabel and mass revealed equivalent elevations in phosphorylcholine and choline, suggesting stimulation of both phospholipase C and phospholipase D activities. To identify the presence of EGF-induced phospholipase D activity, cells were labelled with exogenous [3H]1-0-hexadecyl, 2-acyl phosphatidylcholine and its conversion to phosphatidic acid in response to EGF determined. Radiolabelled phosphatidic acid was detectable in 15 seconds after addition of EGF and was maximal (3-fold) at 30 seconds. Consistent with the presence of EGF-induced phospholipase D activity, treatment of cells with EGF, in the presence of [14C]ethanol, resulted in the rapid formation of [14C]phosphatidylethanol, the product of phospholipase D-catalyzed transphosphatidylation. The formation of phosphatidylethanol, which competes for the formation of phosphatidic acid by phospholipase D, did not diminish the induction of 1,2-diglyceride by EGF. These data suggest that the phosphatidic acid formed by phospholipase D-catalyzed hydrolysis of phosphatidylcholine is not a major precursor of the observed increased 1,2-diglyceride. Thus, the induction of 1,2-diacylglycerol by EGF may occur primarily via phospholipase C-catalyzed hydrolysis of phosphatidylcholine.

A method for the quantitative analysis of molecular species of alkylacylglycerol and diacylglycerol

We describe a method for the quantitative analysis of molecular species of diacylglycerol and alkylacylglycerol as their diradylglycerobenzoate derivatives. Synthetic internal standards were used to provide quantitative determinations of the low levels of diacylglycerol and alkylacylglycerol and their individual molecular species in cultured cells. Diradylglycerols were isolated by thin-layer chromatography (TLC), converted to their benzoate derivatives and separated into subclasses by TLC. The molecular species of each subclass were analyzed by reversed-phase high performance liquid chromatography. Thirty-six species of diglyceride-type molecules were identified in Madin-Darby canine kidney cells. These cells were shown to contain 7.88 nmoles of diacylglycerol and 3.97 nmoles of alkylacylglycerol per mumole of phospholipid. Both subclasses contain predominantly monoenoic and saturated species. This technique should be valuable for studies examining the origin and metabolism of these important intracellular mediators.

Fluoride activates diradylglycerol and superoxide generation in human neutrophils via PLD/PA phosphohydrolase-dependent and -independent pathways

In contrast to the rapid, ethanol-inhibited superoxide generation by the receptor-linked agonist formyl-methionyl-leucyl-phenylalanine (fMLP), fluoride-activated superoxide generation occurs after a prolonged lag, and as shown herein is relatively ethanol-insensitive. We have investigated fluoride-activation of diradylglycerol generation and phospholipase D activity. Fluoride induces a very large increase in diradylglycerol mass (both 1,2-diacylglycerol (DAG) and 1-O-alkyl,2-acylglycerol (EAG)), with kinetics similar to superoxide generation. Unlike fMLP-activated diglyceride generation which is completely inhibited by ethanol, that produced by fluoride is only partially (30%) blocked. When the phosphatidylcholine pool is 3H-prelabeled, fluoride activates both [3H]phosphatidic acid (PA) and [3H]diglyceride generation with similar kinetics. Partial inhibition of the production of these species by ethanol was seen, coincident with the appearance of [3H]phosphatidylethanol, indicating phospholipase D-dependent transphosphatidylation had occurred. The data are consistent with the fluoride activation of PA and diglyceride generation by both phospholipase D-dependent and -independent (presumably phospholipase C) mechanisms.

Phorbol-12-myristate-13-acetate activation of phospholipase D in human neutrophils leads to the production of phosphatides and diglycerides

The contribution of phospholipase D (PLD) to the production of phosphatides (PA) and diglycerides (DG) in phorbol-12-myristate-13-acetate (PMA)-stimulated human neutrophils was studied. Neutrophils were double labeled with 1-O-[3H]alkyl-phosphatidylcholine [( 3H]alkyl-PC) and alkyl-[32P]PC. Upon stimulation with PMA, these cells produced 1-O-alkyl-PA (alkyl-PA) and, in the presence of ethanol, 1-O-alkyl-phosphatidylethanol (alkyl-PEt) both containing 3H and 32P. Lagging behind alkyl-PA and alkyl-PEt formation was the production of 1-O-[3H]alkyl-diglyceride [( 3H]alkyl-DG) and [32P]orthophosphate [( 32P]PO4), suggesting dephosphorylation of alkyl-PA by PA phosphohydrolase (PPH). Furthermore, the PPH inhibitor, propranolol, inhibited the formation of both [3H]alkyl-DG and [32P]PO4, while increasing alkyl-PA levels (containing both 3H and 32P). PMA-induced DG mass accumulation was also inhibited by propranolol. The results of this study demonstrate that PMA activates PLD in neutrophils leading to the generation of PA and that the bulk of the DG mass accumulation is derived from the sequential actions of PLD and PPH on PC.

Continuous phosphorylation of both the 47 and the 49 kDa proteins occurs during superoxide production by neutrophils

Neutrophils stimulated with 4 beta-phorbol 12-myristate 13-acetate release large quantities of superoxide (O2-) and exhibit an intense phosphorylation of two proteins with molecular masses of approx. 47 and 49 kDa. Treatment of unstimulated cells with antagonists of protein kinase C (e.g., staurosporine; 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7)) is known to inhibit both of these phenomena upon stimulation. These antagonists of PKC also cause a rapid cessation of O2- release when added to cells that are already stimulated. In this paper, we report that the addition of staurosporine or H-7 to stimulated neutrophils resulted in a rapid loss of 32P from both the 47 and the 49 kDa phosphoprotein bands, as detected by autoradiography. This suggests that these two proteins may be regulated by a continual cycle of phosphorylation and dephosphorylation in the stimulated cell, with the phosphorylation reactions predominating, or undergo a rapid degradation subsequent to phosphorylation. Either explanation is consistent with the view that protein kinase C activity is necessary to both initiate and maintain O2- production in neutrophils stimulated with tumor promoters.

Protein phosphorylation associated with the stimulation of neutrophils. Modulation of superoxide production by protein kinase C and calcium

Neutrophils and other phagocytic cells of the immune system possess a superoxide-generating oxidase system which is essential for the efficient killing of microbes. The system is activated by a wide variety of stimuli, some of which operate through pathways involving protein kinase C (PKC), while others appear not to. The PKC-dependent pathway is probably the major signal transduction route for most of the stimuli. Alterations in cellular Ca2+ and diglyceride levels can have a pronounced stimulatory effect on this pathway by their ability to synergistically activate PKC. This review discusses PKC, the different interactions of this kinase with the plasmalemma that are important in superoxide production, the synergy between Ca2+ and diglyceride, and the nature of the phosphoproteins involved. Evidence supporting the existence of the PKC-independent pathway is also reviewed.